In the automobile field, and particularly in the field of engine production, the state of the art covers the testing of engines to check engine behavior under conditions which substantially reproduce those of actual use.
The tests are carried out on appropriate equipment which are controlled at least thermally and which comprise at least a test bench.
During the tests, working conditions are reproduced to substantially simulate the actual operating and environmental conditions to which the engine is subjected during normal use.
The tests are extremely important to verify the overall functionality of the engine, and make it possible to carry out different measurements of power, consumption, resistance to stress, etc.
To be more precise, temperature testing, that is, testing the functioning of the engine under conditions of extreme temperature to which the engine may be subjected, is extremely important.
Such tests must be able to verify the behavior of the engine under cold starting conditions. Such tests particularly verify the engines's polluting emissions. This is important, as it is well known that a very high percentage of pollutant gases is emitted when the engine is started cold, and during the time the engine takes to reach its working temperature.
Temperature tests may be carried out according to at least two operating conditions depending on the equipment and the method used.
In one operating condition, the engine must already be mounted on the vehicle.
This solution however has the disadvantage that the whole vehicle must be brought to the testing temperature; the automobile must be placed inside an air conditioned room or other suitable place where the temperature conditions required for the test can be reproduced.
Obviously, this procedure involves a very long time, both to bring the automobile-engine system to the required temperature and especially to cool the system down for the next test to be done.
Another situation is more advantageous. In this situation the engine is tested by itself, that is, it is not mounted on the vehicle. In this case it is coupled with an exhaust brake.
In this case too, the test is made inside a thermostatic room which is, however, smaller.
However, the engine is cooled only in the traditional manner, that is, by means of heat exchange by convection between the surface of the engine and the surrounding air which laps it inside the thermostatic room. Thus, the speed at which the temperature is varied is very slow, as the limits imposed by the process of convection limits this speed.
This contrasts with the operating and economic needs of performing successive cycles of heating and especially cooling as rapidly as possible. Increased rapidity would reduce waiting times between one test and another. However, increased rapidity should be gained without modifying the functional lay-out of the engine so as to ensure that the data obtained can be compared.
Document JP 59-37440 and DE 91 126 54 U show circuits to carry out heat stress on engines which are to be tested on a test bench.
In JP '440 there is an autonomous and separate heating circuit which supplies oil and liquid at temperature to the engine. This prevents the engine from seizing up during the high temperature test cycles.
There is also an autonomous and separate cooling circuit which supplies oil and liquid to the engine to cool it when the engine is stopped at the end of the test.
The presence of the autonomous heating circuit makes the test system complex and not very functional.
Moreover, it drastically increases energy consumption because it has to take the oil and liquid to a high temperature. It also increases installation costs because it needs to include the appropriate pipes with the relative valves and interception commands.
Furthermore, it does not explain how cooling takes place during the functioning of the engine.
Document DE '654 includes an autonomous and separate cooling circuit of the accumulation type. Thus, while the engine functions to perform the test, a part of the circuit for the subsequent rapid cooling accumulates liquid at low temperature to perform the subsequent cooling process.
Moreover, during the functioning of the engine in the test, cooling is carried out by the appropriate heat exchangers which can be adapted to the different engines.
This embodiment of the accumulation-type cooling circuit does not allow use of autonomous and separate cooling plants which accomplish, for example, the complete cooling of the test chamber where the tests are carried out. Nor does this embodiment allow other structures or services complementary and accessory to the test bench.
The use of heat exchangers for cooling purposes during the normal functioning of the engine does not enable testing of the engine in real conditions which completely reproduce actual functioning conditions. This makes the test not completely reliable and incomplete with respect to the effective working of all the components and all the auxiliary circuits of the engine.